Multiple-Polarization Cloaking for Projected and Writing Surface View Screens

ABSTRACT

A system includes a view screen with polarized output. The view screen may include a projected view screen or writing-surface view screen. A window capable of blocking the polarized output at least in part cloaks the view screen to frustrate viewing of the view screen through the window. In some cases, the window includes an array of panels capable of blocking multiple polarizations. The array may disrupt multiple different polarized view screen outputs while maintaining transparency to unpolarized light. In some cases, the window capable of blocking polarized output may be paired with view screen cover that converts view screen output in an unblocked polarization to one of the one or more polarizations blocked by the window.

PRIORITY

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 15/906,617, filed 27 Feb. 2018, Attorney Docket No.15686/153, and titled Multiple-Polarization Cloaking for Projected andWriting-Surface View Screens, which is incorporated by reference in itsentirety.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. Provisional Patent Application Ser.No. 62/515,508, filed 5 Jun. 2017, Attorney Docket No. 15686/82, andtitled Multiple-Polarization Cloaking, which is incorporated byreference in its entirety.

TECHNICAL FIELD

This disclosure relates to visual information obfuscation for polarizedimage sources.

BACKGROUND

Rapid advances in communications technologies and changing workspaceorganization have provided workforces with flexibility in selection anduse of workplace environment. As just one example, in recent years, openplan workplaces have increased in utilization and popularity.Improvements in workspace implementation and functionality will furtherenhance utilization and flexibility of workplace environments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example multiple-polarization cloaking environment.

FIG. 2 shows an example window array.

FIG. 3 shows an example technique for manufacturing a window array.

FIG. 4 shows an example multiple-size-parameter repeated square array.

FIG. 5 shows an example constrained randomized pattern array.

FIG. 6 shows an example repeated triangle pattern array.

FIG. 7 shows an example multiple-size-parameter repeated diamond array.

FIG. 8 shows an example ring array.

FIG. 9 shows an example crossing line array.

FIG. 10 shows an example diagonal crossing line array.

FIG. 11 shows an example letter array.

FIG. 12 shows an example fractal array.

FIG. 13 shows an example multi-scale pattern array.

FIG. 14 shows an example view screen cover and polarizer window.

FIG. 15 shows an example view screen cover and window array.

FIG. 16 shows an example plot of polarization disruption scenario.

FIG. 17 shows an example card with multiple different polarizer panelsand a complimentary technique for polarization determination.

FIG. 18 shows an example aperiodic tiling array.

FIG. 19 shows an example projected view screen system.

FIG. 20 shows an example writing-surface view screen system.

FIG. 21 shows a side view of an example whiteboard-type writing-surfaceview screen.

DETAILED DESCRIPTION

In various environments operators, such as, workers in a workspacepresenting information on a view screen (for example, a television,computer screen, monitor, mobile device screen, teleconferencing screen,projector image, any polarized image source, or other view screen),people communicating in a teleconference, collaborators working in agroup, or other individuals, may display sensitive information (e.g.,private, non-public, confidential or otherwise sensitive material) on aview screen. Increasingly, sightlines in office environments areunobstructed both due to increasing popularity of open plan workplacesand improved construction techniques and architecture that reduce theunderlying support structure footprint of a building which may inhibitsightlines. Accordingly, sensitive information displayed on view screensintended for an intimate audience within a room or other designatedarea, but may be intelligible (e.g., visible, readable, unobstructed, orotherwise observable) outside of the intended audience area. Forexample, unobstructed sightlines may allow viewing into the designatedarea despite an intention to limit viewing from outside the designatedarea.

Accordingly, techniques and architectures for cloaking sensitiveinformation displays without necessarily inhibiting, or at least withoutcompletely obstructing sightlines, will allow for preservation of openplan layouts while maintaining privacy for sensitive information.

When light passes through a polarizer (or polarization filter), thepolarizer will pass light of a particular polarization, while blockinglight in other polarizations. Light polarized orthogonally to the passedpolarization may exhibit the greatest attenuation (e.g., blocking).Accordingly, a polarizer may be described as passing a firstpolarization, as filtering a second polarization, or both.

Polarization may include the spatial orientation of the oscillation ofthe electronic field of travelling electromagnetic wave (e.g., light, orlightwaves). When the oscillation of the field is along a line in theplane transverse to propagation the light may be linearly polarized. Theorientation of the linear polarization may be described by an angle. Forpurposes of explanation, light polarized horizontally and linearly maybe referred to as 0-degree polarization. Accordingly, light polarizedvertically and linearly may be referred to 90-degree polarization and isorthogonal to the 0-degree polarization. Other orientations may bereferred to by their relative angle (e.g., 0 to 180 degrees). When theoscillation orientation rotates (e.g. does not remain along a singleangle) as the electromagnetic wave travels, the polarization may have acircular polarization component. The polarization component may beeither right circular or left circular depending on the direction ofrotation of the electromagnetic wave. Left and right circularpolarizations may be orthogonal to one another. Unpolarized light mayinclude multiple different polarization components. Unpolarized lightmay be converted to polarized light by passing the unpolarized lightthrough a polarizer.

View screens may include various polarized image sources such a liquidcrystal displays (LCDs), light emitting diode (LED) backlit displays,anti-reflective surface displays, organic light emitting diode displays(OLEDs), or other polarized image sources. Natural lighting sources mayinclude unpolarized light sources. Therefore, placing a polarizeroriented to filter out the polarized light from the view screen over awindow (or other transparent panel) in a room may obscure, block, orotherwise render unintelligible light from the view screen whileallowing light from unpolarized sources or other polarizations to passthrough the window. In other words, the light from the view screen isblocked by the polarizer while other light passes through the window, atleast partially.

In some cases, different view screens may have different polarizationoutput types (e.g., 0-degree polarization, 90-degree polarization,45-degree polarization, 135-degree polarization, circular polarization,or other polarization). For example, different view screens may havelinear polarization outputs with different orientations. Accordingly, aparticular polarizer in a particular orientation that blocks output froma first view screen may not necessarily block output from a second viewscreen with different polarization output from the first view screen.However, blocking all possible polarizations (e.g., blocking a firstpolarization and its orthogonal complement polarization) may render atransparent window opaque. Accordingly, generating a single uniformpanel that passively (e.g., without active mechanical rotation) blocksall possible polarized view screen outputs may result in an opaquepanel.

A panel or window capable of multiple-polarization cloaking may beachieved by constructing the panel as a non-uniform array of at leastfirst and second panels, where the first panels block a firstpolarization and the second panels block a second polarization. However,unpolarized light will pass through both sets of panels with onlypartial attenuation. The first and second panels may be interspersed(e.g., interlaced, mixed, or distributed) in an arrangement that, whileallowing some of the polarized image to pass, renders the resultingoutput unintelligible after passing through the array regardless ofwhether the image is in the first or the second polarization. Additionalpanel sets (e.g., third, fourth, . . . , nth panel sets) may beinterspersed with the first and second panel sets to block additionalpolarizations.

The non-uniform array may be made by patterning waveplates (e.g., a waveretarder, a birefringent material, a thin film waveplate, or otherwaveplate) onto a polarizer substrate. The polarizer substrate mayfilter light in a ‘filtered polarization’. The patterned waveplates mayconvert light in polarizations other than the filtered polarization tothe filtered polarization, such that it is blocked by the polarizersubstrate. Individual panel sets may correspond to individual waveplateorientations/thicknesses such that one different polarization is blockedper panel set.

Additionally or alternatively, a window may be constructed to block oneor more pre-determined polarizations. Any view screens that produceimages in unblocked polarizations that are not included within the oneor more pre-determined polarizations may be obscured by converting theunblocked polarizations into the one or more pre-determinedpolarizations. For example, light from a 90 degree polarization outputview screen may be converted into 0 degree polarization by passing theoutput through a waveplate (e.g., a half-waveplate with fast axisoriented at 45 degrees). Accordingly, a waveplate cover may be mountedover view screens, such that a 0-degree polarization filtering panel maybe used to block both the 90-degree polarization output of the viewscreen (after rotation) and 0-degree polarization output from other viewscreens. Other combinations are possible, as discussed below.

Accordingly, multiple-polarization cloaking may be used to preserveinformation privacy over a wide array of view screens using a polarizerpanel that filters one or a pre-determined set of polarization outputs.Thus, multiple-polarization cloaking provides an improvement overexisting market solutions by allowing one panel array or apanel-converter system to deliver information privacy for informationdisplayed on different view screens with different polarization outputswhile allowing light from unpolarized sources to at least partiallypass. Thereby, multiple-polarization cloaking delivers the informationprivacy without necessarily interrupting the sightlines of an open planlayout.

FIG. 1 shows an example multiple-polarization cloaking environment(MPCE) 100. In the MPCE 100, multiple view screens 102, 104, 106generate different polarization outputs 112, 114, 116. The inclusion ofmultiple view screens in the MPCE is done by way of example to show howthe MPCE 100 may handle view screens with different polarizationoutputs. In various implementations, a single view screen or multipleview screens with the same or different polarization outputs may bepresent. The first view screen (View screen A 102) may have A-typepolarization output 112, the second view screen (View screen B 104) mayhave B-type polarization output 114, and the third view screen (Viewscreen C 106) may have C-type polarization output 116. The MPCE mayfurther include non-transmissive walls 199 and a window 108.

The window 108 may include an array with interspersed panels includingA-type blocking panels 122 and B-type blocking panels 124. The A-typeblocking panels 122 may render images from A-type polarization outputunintelligible. The B-type blocking panels 124 may render images fromB-type polarization output unintelligible.

A, B, and C type polarizations may be arbitrary polarizations ofdifferent types. For example, A, B, and C type polarizations may beselected from among common polarization types for view screens,including 0 degree polarization, 90 degree polarization, 45 degreepolarization, 135 degree polarization and circular polarization.

A view screen cover 126 may be mounted over View screen C 106. The viewscreen cover may convert C-type polarization into A-type polarization.For example, the view screen cover may include a waveplate (e.g., a waveretarder, a birefringent material, a thin film waveplate, or otherwaveplate) oriented to convert C-type to A-type. Accordingly, theconverted C-to-A polarization output may be rendered unintelligible bythe A-type blocking panels 122 on the window 108.

Waveplates

Waveplates may be constructed with different orientations and levels ofwave retardance. Light polarization may be characterized as having twooscillating spatial components. The relative phase of the two componentsmay determine the polarization of a lightwave. Accordingly, phasedelaying one two components with respect to the other may alter thepolarization of the light. At one level of retardance, e.g., half-waveor λ/2, the relative phase of the components may be delayed by 180degrees or a half-wavelength. Delaying with a half-waveplate may changethe orientation of linearly polarized light. At another level ofretardance, e.g., quarter-wave or λ/4, the relative phase of thecomponents may be delayed by 90 degrees or a quarter-wavelength.Delaying with a quarter-waveplate may change linearly polarized lightinto circularly polarized light or vice versa. Other retardances may beused to create elliptically polarized light or correct for ellipticalpolarization.

In some implementations, waveplates may be constructed from abirefringent material, e.g., a material with two different indices ofrefraction depending on the direction of oscillation of the e-field. Thetwo different indices may cause different phase velocities for the lightalong two different spatial axes perpendicular to the direction oftravel of the lightwave, e.g., a “fast axis” with a relatively lesserrefractive index and a “slow axis” with a relatively lesser refractiveindex.

In some cases, a half-waveplate may rotate linear polarization by twicethe angle between the fast axis and the angle of polarization of thelight. Accordingly, a half-wave plate at 45 degrees will cause light at90 degrees to convert to 0 degree or vice versa. In another example,half-wave plate at 22.5 degrees will cause light at 45 degrees toconvert to 0 degree. In yet another example, half-wave plate at 67.5degrees will cause light at 0 degrees to convert to 135 degrees.

In some cases, a quarter-waveplate oriented at 45 degrees relative tothe orientation of a linearly polarized lightwave may convert thelightwave to circular polarization. Circularly polarized light incidenton a quarter waveplate produces linearly polarized light at 45 degreesrelative to the quarter-waveplate's fast axis. Accordingly, circularlypolarized light incident on a quarter-waveplate oriented with its fastaxis at 45 degrees may produce 0 degree polarized light. However, anyoutput linear polarization may be achieved by orienting the fast axis ofthe quarter-waveplate.

Window Array

FIG. 2 shows an example window array 200. The example window arrayincludes panel sets of four types 202, 204, 206, 208. The four types areinterspersed to makeup the window array and block four differentpolarizations. In the example window array 200, the panels are square.

In some cases, the array may be constructed by generating the window asa multiple paned (similar to a stained glass construction or tiledconstruction). Window-pane style construction may (in some cases)increase the attractiveness of the array. However, window-paneconstruction may be more complex and potential expensive that otherconstructions.

In some implementations, thin film waveplate panels, e.g., cholestericliquid crystals (CLCs), liquid crystal polymers, VG Smartglass™ or otherthin film waveplate, may be patterned on (e.g. through placement andcuring or deposition) a window substrate (plastic, glass, temperedglass, or other substrate), roll printed and added as an adhesive layerto a polarizer substrate, or laminated between window layers. The thinfilm waveplate panels may be placed on single uniform polarizer pane (orlaminate pane). Accordingly, the multiple panel array may be constructedfrom a single substrate pane.

In some implementations, the window array may be may be fabricated as apatterned waveplate film that may be laminated onto a linear polarizer.In some cases, the linear polarizer may also be a thin film.Accordingly, the patterned waveplate film and linear polarizer may befashioned into a laminate film that may be applied to a glass, plastic,or other transmissive substrate.

Similarly, in some implementations, thin film polarizer materials (e.g.,polyvinyl acetate, stretched polyvinyl alcohol impregnated withpolyiodine, or other thin film polarizer materials) may be used on atransmissive substrate (e.g., optically clear) to construct the array.Polarizer panels blocking different polarizations may be interlaced toform the array.

FIG. 3 shows an example technique 300 for manufacturing a window array.The number of panel sets is selected (302). For example, the window maybe set up to block two or more different polarization types. Some commonview screen polarizations may include 0 degree, 90 degree, 45 degree,135 degree, and circular polarizations. In some cases, one or more ofthese common polarizations may be selected for the one or more panelsets. However, other polarizations may be selected. The arrayarrangement is selected (304). For example, the arrangement may includea checkered pattern, a crossing line pattern, a diagonal crossing linepattern, a fractal pattern, a multi-scale pattern, a repeated ringpattern, a constrained randomized pattern, a letter pattern, a repeatedtriangle pattern, an aperiodic tiling pattern, a security-envelope-likepattern or other arrangement of panels. The arrangement may be selectedsuch that output from a view screen with any of the filter polarizationsmay be rendered unintelligible.

After the arrangement is selected, a panel set may be placed on thearray in accord with the arrangement (306). Once the panel set isplaced, it may be determined whether the selected number of panel setshave been placed (308). If the selected number of panel sets have notbeen placed, additional panel sets may be placed (306). If the selectednumber of panel sets have been placed, the window array may beconstructed (310). For example, the multiple pane or thin filmconstruction techniques discussed above may be used. In a thin filmwaveplate example, the panel sets may be placed and printed on a rollmaterial and then laminated onto a polarizer substrate.

FIG. 4 shows an example multiple-size-parameter repeated square array400. In the multiple-size-parameter repeated square array 400, twoexample square sizes 402, 404 are repeated in afirst-polarization-blocking background panel 406. Accordingly, themultiple-size-parameter repeated square array 400 may accommodate up tothree or more panel sets (e.g. a panel set for the background 406 andtwo for the two different square sizes 402, 404). The multiple-sizeparameters include the different square sizes. In some implementations,the different size parameters may be selected independently from oneanother. For example, the size parameters may be selected based ondisrupting viewing at two different size scales. Additionally oralternatively, the size parameters may selected to create anaesthetically pleasing design.

FIG. 5 shows an example constrained randomized pattern array 500. Theconstrained randomized pattern may include multiple panel types (502,504) placed in a randomized (e.g., random, pseudorandom or othernon-deterministic pattern) arrangement in the array 500. However, insome cases, the randomized placement of the panels may be constrained.For example, the randomized placement may be constrained such that nomore than a maximum area may occur in the array without at least onepanel of every type. In the example constrained randomized pattern array500, panel 506 is forced to be a specific panel type 504 because thesurrounding area has too many panels of the other type 502. Similarly,another panel 508,602 is forced to be the other panel type 502. This mayprevent arrays from having large sections that are unblocked for a givenpolarization.

FIG. 6 shows an example repeated triangle pattern array 600. In theexample repeated triangle pattern array 600, isosceles triangle panels602, 604 are interlaced. However, other triangle shapes may be used. Forexample, equilateral triangles may be organized into tessellatinghexagons and a panel pattern may be formed from the interlacedtriangles.

FIG. 7 shows an example multiple-size-parameter repeated diamond array700. In the multiple-size-parameter repeated diamond array 700, twoexample diamond sizes 702, 704 are repeated in a background panel 706.Accordingly, the multiple-size-parameter repeated square array 700 mayaccommodate up to three or more panel sets (e.g. a panel set for thebackground 706 and two for the two different square sizes 702, 704).

FIG. 8 shows an example ring array 800. Repeating rings 802 cross withinthe array over a background 804. The rings 802 divide the background 804into multiple regions. Accordingly, both the rings 802 and background804 may accommodate one or more panel sets. Circular rings are shown inthe example ring array 800, but other off-circular (e.g., oval,elliptical) may be used.

FIG. 9 shows an example crossing line array 900. The crossing lines 902,904 may have multiple thicknesses, and may divide the background 906into multiple regions. Accordingly, both the crossing lines 902, 904 andbackground 906 may accommodate one or more panel sets.

FIG. 10 shows an example diagonal crossing line array 1000. The diagonalcrossing lines 1002, 1004 may have multiple thicknesses, and may dividethe background 1006 into multiple regions. Accordingly, both thediagonal crossing lines 1002, 1004 and background 1006 may accommodateone or more panel sets.

FIG. 11 shows an example letter array 1100. In the example letter array1100, letters 1102 and other characters 1104 (e.g., letters, numerals,ASCII characters, UNICODE characters, or other characters) may be placedover a background 1106. In some cases, the letters may form words 1108.Words may focus attention on the window array rather than the blockedpolarization image. Additionally or alternatively, letter arrays withdense grouping of multiple-size characters may increase difficultly inresolving particular characters present in a blocked polarization image.Visual mixing between the letter-shaped panels and the content of theblocked polarization image may increase uncertainty when trying todetermine the character content of the blocked polarization image. Inmany cases, sensitive information displayed on a view screen may includetext. Accordingly, array patterns that efficiently disrupt the abilityto read text may be effective in frustrating eavesdropping (e.g.,intentional or incidental).

FIG. 12 shows an example fractal array 1200. In the example fractalarray 1200, the arrangement of panels has features that areself-reproducing on multiple size scales. Accordingly, the arrangementmay disrupt viewing of content from view screens at various size scalesand distances. In some cases, a maximum feature size may be enforced toensure that no region large enough to sustain viewing of a view screenoccurs for any one blocked polarization.

FIG. 13 shows an example multi-scale pattern array 1300. In the examplemulti-scale pattern array 1300, the arrangement of panels has features1302, 1304 at multiple size scales. However, the features may notnecessarily be self-reproducing. Accordingly, the arrangement maydisrupt viewing of content from view screens at various size scales anddistances. In some cases, a maximum feature size may be enforced toensure that no region large enough to sustain viewing of a view screenoccurs for any one blocked polarization. In the example multi-scalepattern array, the pattern is a pixelated pattern with straight-edgedfeatures. However, multi-scale patterns may include patterns with curvededges and no pixelation. Other examples of multi-scale patterns mayinclude CADPAT or MARPAT (e.g., “digicamo”) combat uniforms.

In some implementations, the array may be arranged in accord with amathematical tiling algorithm. Mathematical tiling algorithms mayinclude periodic, aperiodic with n-fold symmetry, aperiodic,pseudorandom, and/or quasi-crystal patterns. In some implementations,tiling algorithms may qualify for membership in one or more of thesegroupings.

In some implementations, tiling patterns may be generated and then thetiles may be assigned to different panel groupings. The different panelgroupings may block different polarizations. By dividing the tilingpattern into multiple groupings, multiple polarizations may be cloakedby the tiling pattern. In some cases, the tiles within the patterns maybe assigned to different grouping based on the shape of the tile, thespatial orientation of the tile in the pattern, a numerical value (e.g.,random, pseudorandom, deterministic, ordinal, or other numerical value)which may be assigned during pattern generation. In some cases,deterministic coloring schemes may be used to generate colorful imagesusing mathematical tiling algorithms. Virtually any such deterministiccoloring scheme for image generation may be used to divide a tilingpattern for multiple-polarization cloaking by assigning colors or groupsof colors to respective polarization filtering panel groups.

In some cases, quasi-crystal mathematical tiling patterns may begenerated using a “seed” input. The seed input may be an initialarrangement of shapes (e.g., starting conditions) from which the tilingpattern is “grown” by the algorithm. In some implementations, thisgrowth processing may share similar pattern recreation characteristicswith the process of crystal growth. The initial seed pattern may be usedto control tile shape and the overall semi-repeating pattern/symmetriesof the quasi-crystal tiling pattern. The base tile shape may includetriangles, rhomboids/squares/rectangles or other quadrilaterals,hexagons, other polygons, or a combination thereof.

Two examples of quasi-crystal tiling patterns may include Penrose tilingalgorithm and Danzer's seven-fold tiling pattern algorithm. In somecases, Danzer's seven-fold tiling pattern algorithm may have a greaterdegree of apparent randomness than Penrose tiling algorithms.

Aperiodic tiling patterns, including quasi-crystal patterns, may includerandom and/or pseudorandom features, while at the same time includingrepeating and semi-repeating features and symmetries. In some cases, thepattern (both random and regular features) may have a physicallydisruptive effect when used to block polarized images. However, theaperiodic tiling patterns may further have a psychologically disruptiveeffect, e.g., such patterns may distract a viewer and draw focus to thepattern rather than sensitive information displayed on a view screenbehind the pattern. In some cases, the intentional nature of therepeated and/or symmetrical features may draw the attention of theviewer, while the random/pseudorandom features cause the viewer toremain focused on the tiling pattern as the viewer attempts to determinewhether the pattern is random. In some cases, aperiodic tiling patternsmay be more aesthetically than purely random patterns.

In some implementations, an aperiodic tiling pattern may disrupt viewingat different distances e.g., different distances from the view screenand different distances between the viewer and the window with theaperiodic tiling pattern. When a viewer is close to the tiling patternthe amplitude (e.g. apparent shape size) of the tiling pattern isgreater than when viewer is far from the tiling pattern. Amplitudefeatures may include tile parameters such as shape variation, sizevariation, orientation variation, other single tile parameters, or anycombination thereof. When a viewer is close to the tiling pattern thefrequency (e.g. amount of pattern visible and repetition of regularfeatures) of the tiling pattern is less than when viewer is far from thetiling pattern. Frequency features may include macro (e.g.,multiple-tile) pattern repetition, macro symmetries, or othermultiple-tile features. In some cases, the level and randomness (e.g.,pseudorandomness) and complexity of the pattern may affect the level ofpsychological disruption experienced by the viewer. Selection of apattern that provides complexity and randomness through amplitudefeatures may provide disruption when the viewer is close to the array.Selection of a pattern that provides complexity and randomness throughfrequency features may provide disruption when the viewer is far fromthe array. Selection of a pattern that provides complexity andrandomness through both frequency and amplitude features may disruptviewing at multiple different viewing distances, or over a range ofviewing distances.

FIG. 18 shows an example aperiodic tiling array 1800. The exampleaperiodic tiling array 1800 includes features of a Danzer's seven-foldtiling algorithm based tiling pattern. The example aperiodic tilingarray 1800 may be derived from a Penrose tiling algorithm. However, inother implementations, a Danzer's seven-fold tiling algorithm may beused to generate a tiling pattern. The multiple (e.g., four) shades usedin the example aperiodic tiling array 1800 represent the differenttiling groups that disrupt images in different polarizations. Theexample aperiodic tiling array 1800 may be decomposed in to examplesub-arrays 1810, 1820, 1830, 1840 by polarization type. In other words,the example sub-arrays 1810, 1820, 1830, 1840 could be super-imposed orstacked on to one another to generate the example aperiodic tiling array1800. In this case, the example aperiodic tiling array 1800 may disruptfour different polarizations (e.g., polarizations A, B, C, D). However,using different tile assignment mechanisms (e.g., coloring algorithms asdiscussed above), greater of fewer polarization types may be blocked.

FIGS. 4-13 and 18 show various examples of patterns that may be used tofrustrate viewing of sensitive view screen content through a windowarray. However, other patterns may be used.

For example, a wealth of patterns have been used for security envelopeinterior designs to frustrate attempts to read unopened mailings. Suchsecurity envelope designs may be adapted to window array designs. Forexample in one adaptation technique, the each of multiple tones used tocreate the security envelope pattern may be assigned individualpolarization to block. The security envelope pattern may be scaled suchthat a person may be able to resolve the security envelope features at adistance (e.g., 1-3 meters) at which a passerby may stand from thewindow array.

As yet another example, multi-tone images of virtually any type may beused. Each of the multiple tones may be assigned a particularpolarization to block. For example, multi-tone images of one or morehistorical figures, flowers, animals, brand insignias, or other imagesmay be rendered in the window array. The images may draw the focus ofthe viewer to the plane of the window array and away from the viewscreen content.

The window arrays may be patterned in liquid crystal polymer (LCP)materials or other materials (such as CLCs), which allow forhigh-resolution waveplate patterning. For example, techniques, such asthose discussed in U.S. Pat. No. 9,122,013, may be used. As discussedtherein: for photopatterned surface alignment, alignment layers mayprovide a defined orientation of liquid crystal (LC) molecules incontact with the aligning surface. A photoaligned layer may be orientedby light exposure, e.g., potentially without any mechanical contact andconsequently enables an arbitrary orientation to be transferred to theLC molecules. Exposing a substrate coated with specializedphoto-reactive polymers (azo-dyes, Rolic Research Linear Photopolymers)to linearly polarized UV light (LPUV) induces preferential alignmentdirection in the direction of polarization and subsequent alignment ofLC molecules coming in contact with the photoreactive alignment layer. Aspatial variation in alignment direction can be induced byarea-selectively exposing the alignment layer to differently conditionedLPUV light, for example, with varying intensities, incidence angles, orpolarization directions. Then, the anisotropic LPP layer may be coatedwith a formulation of the LC pre-polymer containing also aphotoinitiator. After aligning the LC pre-polymer by the subjacent LPPlayer, the film may be cross-linked and polymerized with unpolarized UVlight, providing a permanently oriented patterned retarder.

As further discussed therein: variation in retardance may be achievedthrough thickness patterning of liquid crystal polymer retardancelayers. A liquid crystal polymer may be wet coated on a substrate withuniform alignment layer coated on the substrate. A UV photomask exposuremay be used to photopolymerize specific regions into a planar alignment.The substrate may be then treated with tetrahydrofuran (or otherdeveloper chemical) to dissolve liquid crystal polymer that has not beencross-linked and polymerized. This may result in regions with noretardance and regions of retardance dependent on liquid crystal polymerbirefringence and layer thickness.

As further discussed therein: the wave retarder may be patterned bychanging the thickness of the birefringent material through replicatemold liquid crystal polymer printing. PDMS (polydimethylsiloxane)polymer mold stamps can be created using a master photolithographicallyproduced polymer mold and subsequently used to stamp patterns inpolymeric liquid crystals. The liquid crystal polymer may be cured withthe stamp imprinted into the material leaving a residual patternedliquid crystal retarder. Alignment may be generated through theinteraction of liquid crystal polymer with treated imprinting PDMSsurface such that additional alignment layers are not necessary.

As further discussed therein: the wave retarder may be patterned bychanging the thickness of the birefringent material through coating thematerial on a substrate with varying surface height. To vary the surfaceheight, a micro embossing, e.g., applying a micro patterned stamp andmoldable non-birefringent transparent substrate such as polyethylene(PET) polyvinyl alcohol (PVA) or polyimide, may be sued. This patternedsubstrate may then be peeled from the mold and coated with a printablepolymer liquid crystal or other birefringent material.

As further discussed therein: the wave retarder may be patterned bychanging the birefringence through mixing photoreactive alignment layersdirectly into the liquid crystal polymer mixtures. The alignment of theliquid crystal polymer may be controlled throughout the volume of theliquid crystal polymer mixture. This mixture may be applied to asubstrate with a uniform planar alignment layer. The sample may be UVphotomask exposed in one region with one UV polarization and anotherregion with a different polarization. The different polarizationexposures create a helical or twisted liquid crystal polymer structurewith different chirality (left-handed, right-handed), which in turn maycause different amounts of retardance.

As further discussed therein: the wave retarder may be patterned bychanging the birefringence through photoaligned cholesteric liquidcrystals. Cholesteric liquid crystals (CLC's) have a helical or twistedstructure. CLC's may be engineered such that the amount of chirality (orhelical twisting power) may be modulated through UV light exposure dose,e.g., long exposure to UV may modulate the twist and thus adjust theretardance of a CLC. Patterned retardance layers may be formed throughexposure of different domains of CLC to different dosage amounts of UVlight through multiple photomasks.

Accordingly, a thin film waveplate material (e.g., wave retardermaterial) may be created with adjacent regions with differently orientedfast axes. Accordingly, a half-waveplate region oriented at 0 degreesmay be printed adjacently to a half-waveplate region oriented at 22.5,45, 67.5 or other orientation. Similarly using the techniques discussedabove or other patterning techniques, half-waveplate regions may beprinted densely with quarter-waveplate regions. Using such printing adense array of differing orientation and retardance-level waveplateregions. In some implementations, stamping, printing, or patterningtechniques other than those discussed above with regard to U.S. Pat. No.9,122,013 may be used.

View Screen Cover and Polarizer Window

FIG. 14 shows an example view screen cover 1400 and polarizer window1450. The example polarizer window 1450 blocks light in a specificpolarization (polarization type A). For example, the polarizer windowmay be selected to block 90-degree polarization because displays, insome cases have vertically polarized output. However, virtually anypolarization may be selected for the polarizer window.

The view screen 1402 may generate output in a view screen outputpolarization (polarization type B). If the view screen outputpolarization (e.g., for view screen 1401) is the same as the specificpolarization, the view screen cover 1400 may be omitted.

When the view screen output polarization is different from the specificorientation, the view screen cover 1400 may be mounted using the mount1406 such that it is between the view screen 1402 and the polarizerwindow 1450. The mount 1406 may include an adhesive layer such that theview screen cover may be applied to the view screen's face. Additionallyor alternatively, the mount may include fasteners such that it may beaffixed to the bezel or sides of the view screen and covering thescreen. Additionally or alternatively, the mount may include a windowframe and wall recess (not shown) such that the view screen may beplaced within the recess behind the view screen cover and the viewscreen cover may be held in place by the window frame mount. Virtually,any mount capable of holding the view screen cover 1400 in front of theview screen may be used.

The view screen cover may further include a waveplate with andorientation and retardance level selected to covert the view screenoutput polarization into the specific polarization. For example, if thespecific polarization was 0 degrees and the view screen outputpolarization were 45 degrees, the selected view screen coverhalf-waveplate may have its fast axis oriented at 22.5 degrees. Inanother example, if the specific polarization was 0 degrees and the viewscreen output polarization were 135 degrees, the selected view screencover half-waveplate may have its fast axis oriented at 67.5 degrees. Inanother example, if the specific polarization was 0 degrees and the viewscreen output polarization were left-handed circular, the selected viewscreen cover quarter-waveplate may have its fast axis oriented at 45degrees. For left-handed circularly polarized light, from the point ofview of the source, the direction of e-field rotates clockwise about thedirection of propagation. Similarly, for right-handed circularlypolarized light, from the point of view of the source, the direction ofe-field rotates counter-clockwise about the direction of propagation.Orienting a quarter-waveplate's fast axis at 135 degrees may convertright-handed circularly polarized light to 0 degree linearly polarizedlight. Any half-waveplate may convert right-handed circularly polarizedlight to left-handed circularly polarized light or vice versa.

In some implementations, the polarizer window may include a windowarray. FIG. 15 shows an example view screen cover 1400 and window array1550. The window array 1550 may render unintelligible view screen outputin multiple polarizations (e.g., polarizations types A and D).Accordingly, the view screen cover 1400 may be omitted for view screens1401, 1501 with view screen output in any of the polarization that thewindow array disrupts. Further, the view screen cover 1400 may convertthe view screen output polarization (for view screens 1402, 1502) intoany of the polarizations the window array disrupts. Accordingly, thesame view screen cover 1400 may be used to covert multiple differentview screen output polarizations into disrupted polarizations.

For example, a window array that disrupts two different polarizationsand one view screen cover orientation may be used to disrupt fourdifferent linear polarizations. FIG. 16 shows an example plot 1600 ofpolarization disruption scenario.

In the example scenario, a window array disrupts view screenpolarization output at 45 degrees 1602 and 0 degrees 1604. Accordingly,for view screens with output at 45 degrees or 0 degrees, a view screencover may be omitted. For view screens with output at 90 degrees 1606and 135 degrees 1608 a view screen cover with a half-waveplate orientedat 67.5 degrees 1610 may be used. The view screen cover may convert 1612the 90-degree polarization to a 45-degree polarization, and convert 1614the 135-degree polarization to a 0-degree polarization. If the windowarray instead disrupted at 90 and 135 degrees, the same half-waveplateoriented at 67.5 degrees may instead be used to convert 45 degree and 0degree view screen outputs to 90 and 135 degrees, respectively.

In another example scenario, the window array may disrupt view screenpolarization output at 135 degrees and 0 degrees. Accordingly, for viewscreens with output at 135 degrees or 0 degrees, a view screen cover maybe omitted. For view screens with output at 90 degrees and 45 degrees atview screen cover with a half-waveplate oriented at 22.5 degrees may beused. The view screen cover may convert the 90-degree polarization to a135-degree polarization and the 45-degree polarization to a 0-degreepolarization. If the window array instead disrupted at 90 and 45degrees, the same half-waveplate oriented at 22.5 degrees may instead beused to convert 135 degree and 0 degree view screen outputs to 90 and 45degrees, respectively.

Other combinations, where window-array-disrupted polarizationsorientations along with the converted orientations are symmetric aboutthe orientation of the view screen cover may be used.

In some implementations, an operator may determine the polarization ofthe output of a view screen using a polarization testing device. Oncethe operator determines the polarization of the output, a view screencover, polarizer window, window array or any combination thereof may beselected based on the polarization. Virtually any device that may allowan operator to identify different linear and/or circular polarizationsmay be used.

In some implementations, the polarization determination device mayinclude a card with multiple different polarizer panels. FIG. 17 showsan example card 1700 with multiple different polarizer panels 1702,1704, 1706, 1708, 1710, 1712, and a complimentary technique forpolarization determination 1750. The example card 1700 may include oneor more panels 1702, 1704, 1706, 1708, 1710, 1712 that are filters forpossible polarization output types for view screens. The example card1700 includes a 0-degree filter panel 1702, a 90-degree filter panel1704, a 45-degree filter panel 1706, a 135-degree filter panel 1708, aleft-hand circular filter panel 1710, and a right-hand circular filterpanel 1712. The card 1700 may include indicators 1720 (e.g. identifiersof polarization type, panel indices, or other referenceable indicators)associated with each panel. The operator may view a view screen throughthe card 1700 (1752). The operator may determine the polarization outputof the view screen by determining which panel blocks the view screenoutput (1754). Then the operator may reference the indicator for thatpanel (1756). In various cases where a view screen cover system is used,including after determination of polarization with the card 1700 orother polarization determination device, a view screen cover waveplatemay be selected responsive to the polarization (1758). Once thewaveplate is selected, an orientation for the waveplate may be selected(1760). The operator may mount the view screen cover to the view screen(1762).

The example card 1700 includes panels for 1702, 1704, 1706, 1708, 1710,1712 six different possible view screen outputs. However, panels forother possible polarizations may be included in some implementations.Some implementations, may omit one or more of the polarization typetested by the example card. For example, another example card mayinclude linear polarization types but omit one or more circularpolarization types or vice versa.

In some implementations, one or more of the panels on the card may berotatable. The rotatable panel may include a dial indicator that mayindicate the orientation of the panel. A rotatable panel may be used totest multiple different linear polarization orientations with a singlepanel polarizer capable of being placed in multiple relativeorientations.

Example View Screens

In some implementations, projected and/or writing-surface view screensmay have polarized outputs. For example, a projector may include apolarizer over the output lens of the projector or included within theprojector such that the output of the project includes polarized light.The projector may project the polarized output onto a polarizationpreserving screen, such as a silver-based screen. Accordingly, theoutput may be blocked or rendered unintelligible using theabove-discussed view screen cover system and/or window panel array. Thepolarization orientation of the projector output may be determined usinga polarization determination device, such as the card 1700. In somecases, the polarizer may be extended over the screen. Accordingly,unpolarized projector output light may be polarized once incident on thepolarizing screen. The polarized reflected light may be blocked orrendered unintelligible using the above-discussed view screen coversystem and/or window panel array.

FIG. 19 shows an example projected view screen system 1900. Theprojected view screen system 1900 includes a projector 1902 with anoutput lens 1904. A polarizer 1906 covers the output lens 1904generating output light with polarization type A. The projector 1902 mayproject an image on the polarization maintaining screen 1908. The imageprojected on the polarization maintaining screen 1908 is obscured whenviewed through the window array 1910, which blocks light of polarizationtypes A and B.

In an example, a writing-surface view screen may include a writingsurface such as a whiteboard. The whiteboard may include a backlitwhiteboard, e.g., with incandescent, LED, or fluorescent backlighting,which in some cases may be diffused to generate even lighting across thewhiteboard. The whiteboard may include a polarizer layer that maypolarize the output from the backlighting. A user may write directly onthe polarizer layer, or in some implementations on a substrate, e.g.,such as a polymer layer, forming the front surface of the whiteboard.The polarizer layer and/or front surface may be transmissive in front ofan absorptive background, such that the whiteboard appears black whennot backlit or when the polarized backlighting is cloaked. Writing onthe front surface of the whiteboard may be visible when backlit andinvisible or otherwise obscured when the backlighting is not present orcloaked.

In some cases, cloaking markers may make cloaking marking that arevisible when backlit and invisible or otherwise obscured when thebacklighting is not present or cloaked. Markers may include, e.g.,dry-erase markers, permanent markers, washable markers, pens, pencils,styluses, or other writing utensils. Non-cloaking markers may makenon-cloaking marking that are visible when backlit and still visible orotherwise obscured when the backlighting is cloaked. Any or acombination of cloaking and non-cloaking markers may be used. Forexample, non-cloaking markers may be used to record non-sensitive ornon-classified information on a whiteboard while cloaking markers may beused to record sensitive or classified information on the samewhiteboard.

In some cases, markers that make marks which fluoresce when exposed tolight or marks that alter or remove polarization may be used asnon-cloaking markers with a writing-surface view screen. Markers thatmake marks which do not fluoresce when exposed to light and/or marksthat do not alter or remove polarization may be used as cloaking markerswith a writing-surface view screen. Non-cloaking markers may bemanufactured by constructing writing utensils with pigments thatfluoresce when exposed to light. Such markers may create non-cloakingmarkings that produce light with a polarization not necessarily alignedwith the light incident on the non-cloaking marking. Similarly,non-cloaking markers may be manufactured by constructing writingutensils that generate marks, e.g., via a polymer residue, that removepolarization from light incident on the marking. The removal ofpolarization may frustrate the cloaking process.

Table 1 lists example markers that may be used as non-cloaking andcloaking markers with a writing-surface view screen.

TABLE 1 Cloaking and Non-Cloaking Markers Non- Brand Color CloakingCloaking MAGIC MARKER Red X MAGIC MARKER Green X MAGIC MARKER Blue XSTAPLES Red X STAPLES Black X STAPLES Blue X STAPLES Green X EXPO HighIntensity Red X EXPO High Intensity Black X EXPO High Intensity Blue XEXPO High Intensity Green X EXPO Low Odor Black X EXPO Low Odor Pink XEXPO Low Odor Brown X EXPO Low Odor Cyan X EXPO Low Odor Orange X EXPOLow Odor Blue X EXPO Low Odor Dark Brown X EXPO Low Odor Light Green XEXPO Low Odor Dark Green X EXPO Low Odor Purple X EXPO Low Odor Violet XEXPO Low Odor Red X

FIG. 20 shows an example writing-surface view screen system 2000. Thewriting-surface view screen system 2000 includes a writing-surface viewscreen 2002 that is backlit with polarized light of polarization type A.Markings 2004, 2006 on the surface of the writing-surface view screenmay be made with cloaking and/or non-cloaking markers. Cloaking marking2004 is obscured when viewed through the window array 2010, which blockslight of polarization types A and B. Non-cloaking marking 2006 is notobscured when viewed through the window array 2010.

FIG. 21 shows a side view of an example whiteboard-type writing-surfaceview screen 2100. The example whiteboard-type writing-surface viewscreen 2100 may include a chassis 2102, a backlight 2104, a diffuserlayer 2106, a polarizer layer 2108, and a substrate 2110.

The chassis 2102 may house the backlight 2104, diffuser layer 2106,polarizer layer 2108, and substrate 2110. The chassis may be formed froma material with rigidity such that the backlight 2104, diffuser layer2106, polarizer layer 2108, and substrate 2110 may be housed withoutshifting relative to one another. For example, the chassis 2102 may beformed from aluminum, steel, other metal, plastic, rubber, or othermaterial. The diffuser layer 2106 may diffuse the output of thebacklight 2014 to generate consistent lighting across thewhiteboard-type writing-surface view screen 2100. The polarizer layer2108 may polarize the light output after diffusion by the diffuser layer2106.

The polarizer layer 2108 may be adhered to the inner surface 2112 of thesubstrate 2110. The front surface 2114 of the substrate 2110 may bemarked, e.g., using a marker 2120. The polarized light output from thepolarizer layer 2108 may pass through the substrate 2110, which mayallow viewing of the marks made on the front surface 2114 of thesubstrate 2110. However, cloaking marks may be obscured when thepolarized light output of the polarizer layer is blocked, e.g., by awindow array system or view screen cover system.

Although not shown, systems capable of obscuring only a singlepolarization may be used with the writing-surface view screen systems(e.g., the example writing-surface view screen system 2000 or examplewhiteboard-type writing-surface view screen 2100) or the projected viewscreen systems discussed herein. For example, the window array 2010could be replaced with a single panel blocking only polarization type A.The single polarization obstructing system may be used with cloaking andnon-cloaking markers.

Various implementations may use the techniques and architecturesdescribed above.

A1 In an example, a system includes: a writing-surface view screenincluding: a backlight; a view screen polarizer layer oriented topolarize output of the backlight in view-screen-output polarization; anda front surface configured to accept cloaking markings; aview-screen-mountable waveplate oriented to convert theview-screen-output polarization to a specific polarization; and apolarizer window within a line-of-sight of the writing-surface viewscreen through the view-screen-mountable waveplate, where the polarizerwindow filters the specific polarization to obscure cloaking markings onthe front surface.

A2 The system of example A1, where the view-screen-mountable waveplateis mounted on the writing-surface view screen to form the front surface.

A3 The system of either example A1 or A2, where theview-screen-mountable waveplate includes an adhesive layer.

A4 The system of any of examples A1-A3, where an outer surface of theview screen polarizer layer forms the front surface.

A5 The system of any of examples A1-A4, where: the front surface isfurther configured to accept a non-cloaking marking; and thenon-cloaking marking is configured to generate light in anotherpolarization different from the view-screen-output polarizationresponsive to the output of the backlight.

A6 The system of any of examples A1-A5, where the writing-surface viewscreen further includes a diffusive layer between the backlight and theview screen polarizer layer.

A7 The system of any of examples A1-A6, where the writing-surface viewscreen further includes an absorptive background behind the view screenpolarizer layer, the absorptive background configured to cause thewriting-surface view screen to appear black when: not backlit; or theoutput from the backlight is cloaked.

B1 In an example, a system includes: a polarization maintaining screen;a projector; a projector polarizer disposed between the projector andthe polarization maintaining screen, the projector polarizer oriented topolarize output of the projector in a first polarization to generate anfirst polarization image on the polarization maintaining screen; apolarizer substrate configured to block a filtered polarization; anarray including: a first panel set including waveplates oriented toconvert a first polarization to the filtered polarization, the firstpanel set arranged within the array to obscure first polarizationimages; and a second panel set interspersed with the first panel set,the second panel set arranged within the array to obscure secondpolarization images.

B2 The system of example B1, where the first polarization includes avertical polarization, a horizontal polarization, a 45 degreepolarization, a 135 degree polarization, a circular polarization, or anycombination thereof.

B3 The system of either example B1 or B2, where the first and secondpanel sets are interspersed in a checkered pattern, crossing linepattern, diagonal crossing line pattern, a fractal pattern, amulti-scale pattern, a repeated ring pattern, a constrained randomizedpattern, a letter pattern, a repeated triangle pattern, an aperiodictiling pattern, or any combination thereof.

B4 The system of any of examples B1-B3, where the array further includesa third set interspersed with the first and second panel sets, the thirdpanel set including waveplates oriented to convert a third polarizationto the filtered polarization, the third panel set arranged within thearray to obscure third polarization images.

B5 The system of any of examples B1-B4, where projector polarizer ismounted such that it covers the polarization maintaining screen.

B6 The system of any of examples B1-B5, where projector polarizer ismounted to cover an output lens of the projector.

C1 In an example, a system includes: a writing-surface view screenincluding: a backlight; a polarizer layer oriented to polarize output ofthe backlight in a first polarization; and a front surface configured toreceive a cloaking marking when engaged with a cloaking marker; firstregions placed to render unintelligible the cloaking marking whendisplayed on the front surface, the first regions obstructive to thefirst polarization and transmissive to a second polarization differentthan the first polarization; and second regions interlaced with thefirst regions, the second regions placed to render unintelligible viewscreen output in the second polarization.

C2 The system of example C1, where the first and second regions arearranged in a checkered pattern, crossing line pattern, diagonalcrossing line pattern, a fractal pattern, a multi-scale pattern, arepeated ring pattern, a constrained randomized pattern, a letterpattern, a repeated triangle pattern, an aperiodic tiling pattern, orany combination thereof.

C3 The system of either example C1 or C2, where the first and secondregions overlap at least in part.

C4 The system of any of examples C1-C3, where the writing-surface viewscreen includes a whiteboard.

C5 The system of any of examples C1-C4, where the front surface isfurther configured to receive a non-cloaking marking when engaged with anon-cloaking marker.

C6 The system of example C5, where neither the first regions nor thesecond regions are placed to render unintelligible the non-cloakingmarking when displayed on the front surface.

C7 The system of any of examples C1-C6, where an outer surface of thepolarizer layer forms the front surface.

D1 In an example, a system includes: a writing-surface view screenincluding: a backlight; a polarizer layer oriented to polarize output ofthe backlight in a first polarization; and a front surface configuredto: receive a cloaking marking when engaged with a cloaking marker; andreceive a non-cloaking marking when engaged with a non-cloaking marker;a panel placed to render unintelligible the cloaking marking whendisplayed on the front surface but not render unintelligible thenon-cloaking marking when displayed on the front surface, the panelobstructive to the first polarization and transmissive to a secondpolarization different than the first polarization.

E1 any component of any of the systems of examples A1-A7, B1-B6, C1-C7,or D1.

F1 In an example, a method includes the method implemented by operationof any of the systems or components thereof of any of examples A1-A7,B1-B6, C1-C7, or D1.

G1 In an example, a kit includes any of the components of any of thesystems of any of examples A1-A7, B1-B6, C1-C7, D1, or any combinationthereof.

Various implementations have been specifically described. However, manyother implementations are also possible.

What is claimed is:
 1. A method of manufacture including: designating aset of one or more cloaking markers; providing a writing-surface viewscreen including: a backlight; a view screen polarizer layer oriented topolarize output of the backlight in view-screen-output polarization; anda markable front surface formed by a view-screen-mountable waveplateoriented to convert the view-screen-output polarization to a specificpolarization, where, when the writing-surface view screen is placedwithin a line-of-sight of a polarizer window through theview-screen-mountable waveplate, the polarizer window filters thespecific polarization to obscure cloaking markings, from a cloakingmarker in the set of one or more cloaking markers, on the markable frontsurface.
 2. The method of manufacture of claim 1, where theview-screen-mountable waveplate includes an adhesive layer.
 3. Themethod of manufacture of claim 1, where non-cloaking markings, whenpresent on the markable front surface, light in another polarizationdifferent from the view-screen-output polarization responsive to theoutput of the backlight.
 4. The method of manufacture of claim 1, wherethe writing-surface view screen further includes a diffusive layerbetween the backlight and the view screen polarizer layer.
 5. The methodof manufacture of claim 1, where the writing-surface view screen furtherincludes an absorptive background behind the view screen polarizerlayer, the absorptive background configured to cause the writing-surfaceview screen to appear black when: the backlight is off; or the outputfrom the backlight is cloaked.
 6. The method of manufacture of claim 1,where the set of one or more cloaking markers includes a non-fluorescingmarker.
 7. A system including: a writing surface view screen; and apolarizer window, the writing-surface view screen including: abacklight; a view screen polarizer layer oriented to polarize output ofthe backlight in view-screen-output polarization; and a markable frontsurface formed by a view-screen-mountable waveplate oriented to convertthe view-screen-output polarization to a specific polarization; adesignation specifying a set of one or more cloaking markers; and thepolarizer window configured to filter the specific polarization toobscure cloaking markings, from a cloaking marker in the set of one ormore cloaking markers, on the markable front surface when within aline-of-sight of the markable front surface.
 8. The system of claim 7,where the view-screen-mountable waveplate includes an adhesive layer. 9.The system of claim 7, where non-cloaking markings, when present on themarkable front surface, light in another polarization different from theview-screen-output polarization responsive to the output of thebacklight.
 10. The system of claim 7, where the writing-surface viewscreen further includes a diffusive layer between the backlight and theview screen polarizer layer.
 11. The system of claim 7, where thewriting-surface view screen further includes an absorptive backgroundbehind the view screen polarizer layer, the absorptive backgroundconfigured to cause the writing-surface view screen to appear blackwhen: the backlight is off; or the output from the backlight is cloaked.12. A system including: a writing-surface view screen including: abacklight; a polarizer layer oriented to polarize output of thebacklight in a first polarization; and a markable front surface; adesignation specifying a set of one or more cloaking markers; firstregions placed to render unintelligible a cloaking marking, from acloaking marker in the set of one or more cloaking markers, whendisplayed on the markable front surface, the first regions obstructiveto the first polarization and transmissive to a second polarizationdifferent than the first polarization; and second regions interlacedwith the first regions, the second regions placed to renderunintelligible view screen output in the second polarization.
 13. Thesystem of claim 12, where the first and second regions are arranged in acheckered pattern, crossing line pattern, diagonal crossing linepattern, a fractal pattern, a multi-scale pattern, a repeated ringpattern, a constrained randomized pattern, a letter pattern, a repeatedtriangle pattern, an aperiodic tiling pattern, or any combinationthereof.
 14. The system of claim 12, where the first and second regionsoverlap at least in part.
 15. The system of claim 12, where thewriting-surface view screen includes a whiteboard.
 16. The system ofclaim 12, where the markable front surface is further configured toreceive a non-cloaking marking when engaged with a non-cloaking marker.17. The system of claim 16, where neither the first regions nor thesecond regions are placed to render unintelligible the non-cloakingmarking when displayed on the markable front surface.
 18. The system ofclaim 14, where an outer surface of the polarizer layer forms themarkable front surface.
 19. The system of claim 14, where the set ofcloaking markers includes non-fluorescing markers.
 20. The system ofclaim 14, further including another designation specifying a set ofnon-cloaking markers.